gpio-led-overlay.dts

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * gpio-led - generic connection of kernel's LED framework to the RPI's GPIO.
 * Copyright (C) 2021 House Gordon Software Company Ltd. <assafgordon@gmail.com>
 *
 * Based on information from:
 *   https://mjoldfield.com/atelier/2017/03/rpi-devicetree.html
 *   https://www.raspberrypi.org/documentation/configuration/device-tree.md
 *   https://www.kernel.org/doc/html/latest/leds/index.html
 *
 * compile with:
 *   dtc -@ -Hepapr -I dts -O dtb -o gpio-led.dtbo gpio-led-overlay.dts
 *
 * There will be some warnings (can be ignored):
 *  Warning (label_is_string): /__overrides__:label: property is not a string
 *  Warning (unit_address_vs_reg): /fragment@0/__overlay__/led_pins@0:
 *                                 node has a unit name, but no reg property
 *  Warning (unit_address_vs_reg): /fragment@1/__overlay__/leds@0:
 *                                 node has a unit name, but no reg property
 *  Warning (gpios_property): /__overrides__: Missing property
 *                 '#gpio-cells' in node /fragment@1/__overlay__/leds@0/led
 *                  or bad phandle (referred from gpio[0])
 *
 * Typical electrical connection is:
 *    RPI-GPIO.19  ->  LED  -> 300ohm resister  -> RPI-GND
 *    The GPIO pin number can be changed with the 'gpio=' parameter.
 *
 * Test from user-space with:
 *   # if nothing is shown, the overlay file isn't found in /boot/overlays
 *   dtoverlay -a | grep gpio-led
 *
 *   # Load the overlay
 *   dtoverlay gpio-led label=moo gpio=19
 *
 *   # if nothing is shown, the overlay wasn't loaded successfully
 *   dtoverlay -l | grep gpio-led
 *
 *   echo 1 > /sys/class/leds/moo/brightness
 *   echo 0 > /sys/class/leds/moo/brightness
 *   echo cpu > /sys/class/leds/moo/trigger
 *   echo heartbeat > /sys/class/leds/moo/trigger
 *
 *   # unload the overlay
 *   dtoverlay -r gpio-led
 *
 * To load in /boot/config.txt add lines such as:
 *   dtoverlay=gpio-led,gpio=19,label=heart,trigger=heartbeat
 *   dtoverlay=gpio-led,gpio=26,label=brain,trigger=cpu
 */

/dts-v1/;
/plugin/;

/ {
	compatible = "brcm,bcm2835";

	fragment@0 {
		// Configure the gpio pin controller
		target = <&gpio>;
		__overlay__ {
			led_pin: led_pins@19 {
				brcm,pins = <19>; // gpio number
				brcm,function = <1>; // 0 = input, 1 = output
				brcm,pull = <0>; // 0 = none, 1 = pull down, 2 = pull up
			};
		};
	};
	fragment@1 {
		target-path = "/";
		__overlay__ {
			leds: leds@0 {
				compatible = "gpio-leds";
				pinctrl-names = "default";
				pinctrl-0 = <&led_pin>;
				status = "okay";

				led: led {
			                label = "myled1";
					gpios = <&gpio 19 0>;
			                linux,default-trigger = "none";
				};
			};
		};
	};

	__overrides__ {
		gpio =       <&led>,"gpios:4",
		             <&leds>,"reg:0",
		             <&led_pin>,"brcm,pins:0",
		             <&led_pin>,"reg:0";
		label =      <&led>,"label";
		active_low = <&led>,"gpios:8";
		trigger =    <&led>,"linux,default-trigger";
	};

};